FIG. 1A illustrates a heart 10 with a partial internal view and arrows indicating the direction of blood flow within the heart. Four valves in the heart 10 direct the flow of blood within the left and right sides of the heart. The four valves include a mitral valve 20, an aortic valve 18, a tricuspid valve 60, and a pulmonary valve 62 as illustrated in FIG. 1A. The mitral valve 20 is located between the left atrium 12 and the left ventricle 14. The aortic valve 18 is located between the left ventricle 14 and the aorta 16. These two valves direct oxygenated blood coming from the lungs, through the left side of the heart, into the aorta 16 for distribution to the body. The tricuspid valve 60 is located between the right atrium 22 and the right ventricle 24. The pulmonary valve 62 is located between the right ventricle 24 and the pulmonary artery 26. These two valves direct de-oxygenated blood coming from the body, through the right side of the heart, into the pulmonary artery 26 for distribution to the lungs, where it again becomes re-oxygenated and distributed to the mitral valve 20 and the aortic valve 18.
The heart valves are complex structures. Each valve has “leaflets” that open and close to regulate the direction of blood flow. The mitral valve 20 has two leaflets and the tricuspid valve 60 has three leaflets. The aortic 18 and pulmonary 62 valves have leaflets that are referred to as “cusps,” because of their half-moon like shapes. The aortic 18 and pulmonary 62 valves each have three cusps.
During diastole, the leaflets of the mitral valve 20 open, allowing blood to flow from the left atrium 12 to fill the left ventricle 14. During systole, the left ventricle 14 contracts, the mitral valve 20 closes (i.e., the leaflets of the mitral valve 20 re-approximate), and the aortic valve 18 opens allowing oxygenated blood to be pumped from the left ventricle 14 into the aorta 16. A properly functioning mitral valve 20 allows blood to flow into the left ventricle and prevents leakage or regurgitation of blood back into the left atrium (and subsequently back into the lungs). The aortic valve 18 allows blood to flow into the aorta 16 and prevents leakage (or regurgitation) of blood back into the left ventricle 14. The tricuspid valve 60 functions similarly to the mitral valve 20 to allow deoxygenated blood to flow into the right ventricle 24. The pulmonary valve 62 functions in the same manner as the aortic valve 18 in response to relaxation and contraction of the right ventricle 24 (i.e., to move de-oxygenated blood into the pulmonary artery 26 and subsequently to the lungs for re-oxygenation).
During relaxation and expansion of the ventricles 14, 24, (i.e., diastole), the mitral 20 and tricuspid 60 valves open, while the aortic 18 and pulmonary 62 valves close. When the ventricles 14, 24, contract (i.e., systole), the mitral 20 and tricuspid 60 valves close and the aortic 18 and pulmonary 62 valves open. In this manner, blood is propelled through both sides of the heart (as indicated by the arrows of FIG. 1A). The chordae tendineae are tendons linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. As the papillary muscles contract and relax, the chordae tendineae transmit the resulting increase and decrease in tension to the respective valves, helping them to open and close properly. The chordae tendineae are string-like in appearance and are sometimes referred to as “heart strings.” FIG. 1B illustrates an enlarged view of the mitral valve region of the heart with leaflets 25, 26 forming a coapted surface to prevent backflow of blood into the right atrium 12 from the left ventricle 14. Leaflet 26 is tethered by chordae 30, 31 to papillary muscle 27, and leaflet 25 is tethered by chordae 32, 33, and 34.
Regurgitation is a condition in which leaflets of a heart valve do not close completely, resulting in the backflow of blood. For instance, in a condition typically referred to as mitral valve regurgitation, the leaflets of the mitral valve do not close completely during systole and blood leaks back into the left atrium. Studies have shown that one effect of mitral valve regurgitation is the distortion or displacement of the left ventricle, as well as the papillary muscles to which the mitral valve leaflets are attached by the chordae. Displacement of the papillary muscles away from the mitral valve annulus tethers the leaflets into the left ventricle, thereby preventing the leaflets from closing effectively. FIG. 1C illustrates an enlarged view of the heart as shown by FIG. 1B, but with papillary muscle 27 displaced further down in left ventricle 14. Because of the displacement of papillary muscle 27, chordae 34 pulls on leaflet 25 eliminating the coapting surface between the leaflets. This allows oxygenated blood to flow back into the left atrium 12, and the heart is then forced to work harder to pump enough oxygenated blood to the body. This may lead to heart damage over a period of time. Regurgitation is common, occurring in approximately 7% of the population. Mitral valve regurgitation may be caused by a number of conditions, including genetic defects, infections, coronary artery disease (CAD), myocardial infarction (MI), or congestive heart failure (CHF).
Faulty or defective valves may be treated with various surgical procedures. Annuloplasty, for example, reduces the annular size of the mitral valve by placing a synthetic ring around the rim of the mitral valve. These types of procedures are typically major, invasive surgical procedures that may require opening the chest by sternotomy, making incisions in the chest wall, heart-lung bypass and suspending the beating of the heart. These invasive procedures subject patients to a tremendous amount of pain and discomfort and require lengthy recovery and/or hospitalization periods. Patients with congestive heart failure may not be able to tolerate the surgical procedures, leaving them with little or no alternative to treat their defective heart valves. Moreover, reducing the annular size alone may still leave the patient with regurgitation symptoms because the mitral valve leaflet may still be tethered by chordae to the displaced papillary muscles and ventricular walls.